Oceans, Space-Time Stiffness & Ganymede's Hidden Crater: A Cosmic Q&A

Hi there, thanks for joining us again. This is Space Nuts, a Q and A edition. My name is Andrew Dunkley, your host. It's good to have your company. Questions today coming from Matt, who wants to talk about the oceans on Earth. Doug is asking about the stiffness of space time. We have talked about that before, but he's got a different idea. John is asking questions about a new antenna array, and Rusty is honing in on something we talked about late last year, the largest impact crater. He wants to go further than the surface of the Earth. So we'll talk about all of that on this episode of. Space Nuts fifteen second Channel ten nine ignition sig on Space Nuts NI or three two Space Nuts as when I report it, Neil's good and he's done all his homework. He's ready to go. It's Professor Fred Watson, astronomer at LA TE Right. I've just realized there was one bit of homework that I didn't do, which mind it will be all right. Well, it's a thing called guessing. We can do that. We can do that. That'll solve it. Shall we just get straight into it? I think we all too, Yes, I think that would be a very good thing to do. All right. Our first question is a text question from Matt High, Andrew and Fred. I have a question for you. That's good because this is the Q and A segment, so it's good that you've got a question. I was thinking about what the Earth's surface would look like as a rocky planet without any water. Imagine if you happen to live by the sea and could stand on the surface, how different you're part of the world would suddenly look. You'd probably fall a long way too in some parts of the world. That started me thinking, what is it that determines how far our oceans got filled up? Why, for instance, aren't there smaller and why aren't they much smaller and only a max of say a few hundred meters deep. What's the physics that governs how much total water we ended up having on Earth? And if you can share some wisdom on that, it would be grand. Thank you. I love the podcast, been listening for a few years. But this is my first question. Keep up the good work. Thanks Matt, well thanks for sending in the question. We've talked about how. Water ended up on Earth, and there are all sorts of Initially the thought was it's carried by asteroids, but then they started thinking, know that they wouldn't carry enough. And the latest theory is that when the accretion of the planet happened. The water was already there, which would. Probably go a long way to answering Matt's question about how come there's this much. Yes, maybe that's right. In fact, you probably answered it in that regard, although I think the astroid and comet theory still carries weight and holds water. It holds waters. I was avoiding that term. The thing that put doubt on that was the mixture between heavy water and normal water, the isotope ratio, because that mixture in the earth sotionis doesn't really match what we find in comets because we can analyze the vapors that they give off when when they get near the sun. And I mean, in fact, we brought samples back from certainly from asteroids. So but you're right. I think the prevalent idea is that the water was intrinsic to the Earth's formation and maybe it just got topped up a bit by asteroids and comets. So that does. To some extent answer the question. It is to do with the you know, with the inherent mix molecular mix of the constituents of the cloud of gas and dust from which the Earth and the Sun and the Solar System were formed. I think it's not necessarily a done deal though, because we think about some of the ice moons of the Solar System, which are effectively covered in water. They have far more water than the Earth has in its oceans. And I'm talking now about places like Europa, like Titan Saturn's moon, Titan juice to Moon Europa. These are ice worlds, have got a liquid water ocean with a covering of solid ice on top of that. So they're basically global water worlds, except they're covered with ice. So a bigger world of that kind would have a global ocean. And we when we're talking about K two eighteen B, that planet whose atmosphere has shown some possible biomarker chemicals. One of the possible scenarios on K two eighteen B is a world that is actually covered in water, that it's a global ocean, that it's got a thick enough atmosphere that the atmospheric pressure balances out the water surface. So you've got the situation like we have on Earth, where you've got equilibrium between the liquid and the atmosphere. So it may be that, you know, our Earth could have had more water. Maybe some of it's evaporated, maybe some of it has dissociated into its component chemicals, component elements hydrogen and oxygen, which have been lost into space, as we think has happened on the planet Mars. So maybe you know, there is certainly snowball. Earth is one of the things that we think happened in the history of our planet, that it was covered with ice, with an icy surface. It's a great question that that asks, though, about you know what the Earth will be like if you imagined it without the ocean? Those trenches. What's the deepest one eight kilometers or something like that, Yes, and Andreas, I think yes, which will be pretty impressive. Yeah, can you imagine the Earth without water? Yes, Andreas, No. It's not. And it's the what's it called Pacific Trench? Yes, it's a Pacific one. I don't remember. Either, the Marinara Trench. That's the one. Yeah, it's. It's incredibly deep. It's about. Yeah, I'm just trying to find it now. Yeah, if you imagine Earth without water, you could do some incredible sky diving there I reckon without having to catch a plane. Yeah, but getting out that would be the fun part, I imagine. But yeah, it's I can't find the depth of it, but it is. It is something massive. But they have sent submarines down deep into it. Yes, with other people on board. Yeah. Here it is twenty six eight hundred and fifty feet or eight one hundred and eighty four meters deep. What I said, Yeah, you're right, you're doing very well. So, Matt, if the Earth did not have oceans. It would look very, very different. It would be quite spectacular in places, to say the least, because there are mountain ranges under there the ocean which we can't see. Yeah, and even you've got you've got things like Hawaii, which is a super volcano, but you can only see the tip of it. Yes, I do wonder though. It's so you know, there are significant differences. So plate tectonics is the key thing here. The ocean plates are different from the continental plates, and possibly a lot of that is the fact that they're being weighed down by the water, and so without the water they might bounce up a bit and you might get a much more level playing field compared with what it's like now. Well you see evidence of that around New Zealand where the Milford Sound and all the other and Dusty Sound and all those beautiful areas are they're still lifting after the ice Age where the glaciers compressed the ground, and you can see evidence of the rebound effects. So, yeah, you're right because the water ways, I don't know how you'd measure it, but it's incredibly heavy, it's and putting a lot of pressure on those areas. Yeah, the Earth could look very different if all the water disappeared, and it probably bounced back pretty quickly. Yes, in this in geological time, that's right, Yes, yes, absolutely, Thanks for the question, Matt, Howpe we adequately answered that for you. Our next question is an audio a question from Doug Hi. This is Doug and Hazel the Wonder Doodle calling from Whitby, Ontario, Canada. Second time caller. Thanks very much for the show. The question today from Hazel is we've heard people talk about the stiffness of space time being something like one hundred billion billion times stiffer than steal and we're wondering how that can be when space time doesn't matter, so to speak, How can you measure the stiffness of space time, and what exactly are you measuring? Thank you? How long is a piece of string? It's a great question, and I appreciate that one because this is one that has always fascinated me. So what you do is you look at the way matter distort space. And we know that very very well from Einstein's general theory of relativity. We know what the distortion is for a given amount of mass and a given size. That's why we understand black holes because of the fact that the space is so highly distorted. So what you do you look at the way matter distort space, and from that you can determine a property called the Young's modulus of space, which is a kind of geometrical property. It's usually applied to solids as exactly as Doug has said, you know, how can you measure its stiffness when it's. Not a solid. So what you do is you know that it's flexible. You can see the way matter flexes it, and you go from there to saying if it was a solid, it would have this property. And the property we measure is something called Young's modulus. I remember doing Young's modulus as a physics experiment at school. You hang weights on a bit of wire and that gives you the amount of stretch, the stiffness of the wire with the weights hanging on it, and so you can do an equivalent thing. And it's exactly the number actually that that dog has said. It's one hundred billion billion times stiffer than steel ten to the power twenty. There is a there's a paper. It's pretty easy to find it on the web. It was written by let me see if I can bring it up. It is by Kirk T. MacDonald who's at Princeton University. So this is probably the you know, the almost the headquarters of gravity, because that's where where Einstein did a lot of his work. He's he's got a little paper that you can find online what is the stiffness of space time? And the answer I've given is the classical answer, the tenth to power twenty. He's got a quantum answer as well, and you can throw in something about cosmological sound waves and electromagnetic waves and enjoy yourself with some of the equations there. But that's basically where that number comes from. It comes from that paper. Yeah, And it's not so much about the physical attributes of the universe. It's about the fabric of space time itself and. The way it behaves. Yeah, yeah, because we have talked about it before, and I think when we first talked about it, I was quite astonished by how stiff space is. Yes, in the scheme of things, but when you compare it to steel, I guess it puts you in a mindset of a physical thing. Yeah, that's right, like an object, But that's not really what it's about, all right, short answer, but there's yeah, that's pretty well documented. And yeah, you can even certainly look that article up, Doug and learn more about it. And thanks for the question, and thanks for introducing us to your puppy dog. This is Space Nuts Andrew Dunkley with Professor Fred Watson, a Q and A edition. If you're heading overseas soon and you want to be able to get data on your mobile service or your cell phone while you're in another country, you're probably thinking, well, you know, how can I do it? How can I get reliability? How can I get something that's not going to break the bank. 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You can pick a country that you're going to from Afghanistan right through to Zimbabwe and everything in between, or you can get a region. Now, getting a package for a region is a really great idea because you can go to several countries within that area and you're covered. And the prices that are very according to which package you get and where you're going. But you know it is very very inexpensive. Prices very of course, but there's an exclusive. Deal right now. You can get this at salee dot com slash space Nuts and don't forget the code space Nuts at the checkout for a fifteen percent discount. Grab your deal today at sale dot com slash space nuts. Get an e SIM at rockbottom prices. They've cut the prices for space Nuts listeners and all you have to do is go online to sale dot com slash space nuts and find the package that works for you from our sponsor, Saley Murder Spacemuts. Our next question comes from John I live in Cloudcroft, New Mexico, in the United States. Today's Albuquerque New Mexico newspaper reported on NGVLA it will replace an existing twenty seven and TENA array with one hundred and ninety two each new foundation, four hundred and thirty tons, each new antenna generating one point five terror bytes per second, and each eighteen meter tall structure weighing one hundred and thirty tons. How will this new antenna fit into the astronomy community, and he makes a reference to the square kilometer Array and Meercat arrays that are being set up in Australia and South Africa. Thank you, John, I didn't know about this one. Yeah, it's been in the pipeline quite a while. So the VLA is the very large Array in New Mexico. We visited it a few years ago, a very impressive set of antennas, and essentially it's been a really productive machine for research. The VLA back going back to the nineteen seventies, and there's a note on their website that says it's been used for more than eleven thousand different observing projects and had an impact on nearly every branch of astronomy. So what has happening, what is happening now is an upgrade to make it the next generation very large array, the n GVLA, and exactly as John says, it's got similarities actually to the mid frequency component of the square kilometer array, which is in South Africa and is basically an extension of MEERCAP, which is an existing array in South Africa. So that also will have antennas about two hundred, much the same as the ng VLA. Will have what I was looking for. This is a bit of homework that I didn't actually do. It's it's it's going to have a frequency range which I am not sure about. It's probably quite similar. One point two gigahertz or twenty months in amis to one hundred and sixteen gigaherts. Okay, that's rather more, I think, the than the mid frequency of the of the Square Elementary Observatory. I think though, the other thing is that the ng VLA will have a much wider spacing of the antennas. They're talking about over nearly nine thousand kilometers. So this is continent why stuff, and that's certainly bigger than the array in South Africa, and so it will probably be used for different signs. So the answer to John's question is that, yes, these things do dovetail together, maybe in frequency and in spacing, in antenna spacing. It's the sort of thing that astronomers, you know, they don't tend to work in isolation. They have complementary things. And it's a bit like the three ELTs that are currently being planned or built. Extremely large telescopes. These are optical telescopes in the twenty to thirty meter class, and well, there's only one of them that's anywhere near completion, and that's the European extremely Large Telescope thirty nine meter instrument. But there are two others that are still on the stock. So I don't know how the current funding situation in the US will affect them because they require a huge component of u US funding even though they're international projects. They're the Giant Magellant Telescope and the and the TMT the thirty meter telescope in YI, so that it's a similar situation. I think you've got differences. There are nuances of differences between them. They will have different strengths in terms of their capabilities, and the astronomical community throughout the world we'll be glad to have them because the one thing that we're always short of is is astronomical facilities. Telescopes are rare things when it comes to this, you know, things of this size, of this stature. So great to welcome the n g v l A into the you know, into the mix. Yeah, they say the arrail achieve high surface brightness, sensitivity and high fidelity imaging on angular scales down to the milli arc second, and it will extend out to one thousand kilometers and it'll have longer baselines or across North America and Hawaii. Yeah, it's just pretty amber out. Longer comes from I mean that we've seen this already with the you know, the Events Horizon telescope, which goes over basically the diameter of the Earth is the is the baseline for that, But it's only that that's on the nine telescopes or something like that, or nine observatories. Yeah, I mean, I think it's great that they can integrate so much hardware over such vast distances to make them you know, super telescopes basically, and they're so much more powerful and the other data will be very interesting. I'm sure we'll be talking about it at some stage. John, So keep your ear to the podcast platform that you use and there will be more. Thanks for the question. Let's take a little break from the show to tell you about our sponsor, Insta three sixty. I'm going to tell you about their new camera. Just keep in mind as a space Nut's listener, there's a special offer for you, and we'll tell. You about that in a little while. But Insta three sixties new camera is very exciting. It's their new flagship three hundred and sixty degree camera and it does exactly what it sounds like it does. It can take footage in three hundred and sixty degrees. All you have to do is push record and it'll do the rest. And it does it in eight K eight K, and they've also enhanced the low light performance so you'll get outstanding images day or night. If you're a thrill seeker and you love to jump off cliffs and you want a good camera to do that, this will do it for you. If you like to go to deep sea diving, you can do that with this camera. If you just want to take a great camera on holidays, it'll do that brilliantly. 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All you have to do is head to store dot Inster three sixty dot com and use the promo code space nuts. Very important store dot instat three sixty dot com and use the promo code space nuts and that deal with the invisible selfie stick available for the first thirty standard package purchases only. And if you want more information, check out our show notes. But just remember the urlstore dot Insta three sixty dot com and the promo code space nuts. Now back to the show. Okay, we've tacked all four systems space Nuts. The one final question that this one comes from You'll never guess Rusty and Donnybrook Well, Fred Andrew, it's rusty and Donnybrook, Andrew, it's good to have you back. But didn't iidly do a great job in your absence? How did you find it? Questions about the largest. Crater in the Solar System. I presume that the one you spoke about last September on Ganymede. At sixteen hundred kilometers diameter, is larger. Than the one on the Moon the eight conbas So the title of the largest would then change to the word I anime? Does it have a name yet? And I'm just wondering about Triton. It's odd shape would have to have come from an impact decision collision, and I'm wondering if that qualifies as a creator. It's about it took away about a third of the Moon that impact, and was that impact with the planet or did it acquire its odd shape by hitting something else? Thanks guys, cheez, thanks for us. He always good to hear from you, chucking his curveballs. I answer his first question, how do we find Heidi? Heidi found us. Heidi was a Space Nuts listener and she came to us to say, look, I got an idea and I just want to sort of go to school off you guys to find out how I can get my idea out there. And her idea was a podcast about the relationship between real life and science fiction. And I said, well, why don't I introduce you to Hugh in the studio if you can find him and see what happens. And while a Hide's podcast became one of the bytes dot com Stable Reality Check the Science of Fiction podcasts, So that's how it happened. Heidi just sort of wanted to find out how she could get her idea out there, and we took her on, simple as that. So yeah, it turned out to be a really great podcast series. Too, if you want to look it up. And listen to some of the great concepts that science fiction can give to real life situations or vice versa. Sometimes they're a little bit out there and it would never be real. But and she speaks to experts in the field about the ideas of science fiction and whether or not they're feasible in real life. Brilliant, brilliant. Yes, she did fabulous job. While I was always so very pleased to be able to take a break and not have to have any worries at all about friend's behavior. Now now the largest impact crater. We did talk about that recently, and I've forgotten the nuts and bolts of Rusty's question now, but I'm sure you've done your homework for it. It. I have two parts to us this question. One is he talks about and to go back to our podcast of the fourth of September last year to find out what we actually said. But yes, it was a story that there is evidence on Jupiter's moon Gunnymy, the biggest moon in the Solar System, that sometime in the past it was hit by an asteroid, probably a big one hundred kilometers in diameter, which would have created a creator about somewhere between fourteen hundred and sixteen hundred kilometers wide on Ganymede. That's a very very big chunk of Ganymede. Now that crator doesn't no longer exist, it's long gone. Ganymede has a surface that's probably icy and is being renewed all the time by probably you know, the activity maybe even guys as of ice as we see on Europa and then cellared Us, so that crater isn't there anymore. And the reason why we did that story and what has led to the idea that there was this cloud of Ganymede back in the distant past, about four billion years ago. Was what they were saying was concentric circles which are in the surface of Ganymede. So these concentric circles which are all centered on a point which is where that impact is thought to have taken place. So there's no crater, but there are these ancient pieces of evidence of there having been an impact, that these concentric circular features which are quite prominent on Ganymede's surface. So I think the eight and South Pole Basin still has the record for the biggest crater, certainly one of the biggest craters in the Solar system. It's two and a half thousand kilometers in diameters, so it's actually bigger than what the Ganymede crater would have been had it still been there. That's amazing. Yes, So it's a big dip in the southern polar region of the Moon and again thought to be due to an asteroid impact perhaps in the very earliest history of the Moon four billion years ago or so. Now what can I can I glean as to how large that asteroid would have been that hit the Moon? Uh? Yes, I can't remember what the figure is though. It's it's it's sort of almost like a planetary body. It's almost a protoplanet or something like that. So several hundred kilometers across probably yeah, Okay. The second part of Ross's question has me very puzzled because he talks about Triton, which is the biggest moon of Neptune, and it it is uh, it's it's just well, what the the what what ROSSI is saying is that it's got a big impact crater on it to make it a very odd shape. But actually Triton's almost perfectly spherical. So I'm not quite sure what is thinking of and whether he and I are at cross purposes here, whether he's thinking of another object. But Triton is a very well behaved moon. It's in terms of its shape, it's pretty spherical. It's a large moon. It's unusual in that it orbits Neptune backwards. It's what's called a retrograde orbit. It's clockwise a scene from above the North Pole, which is backwards compared with the rest of the Solar System, and so it's it's probably was once a dwarf planet in the Koiker Belt. So it's something that's been captured by the gravity of Neptune. But it is nicely circular, nicely spherical. So not sure about the impact crater. We might talk too Rusty again about that. Yeah, he's not. I'm not sure he'll ever send a question in again. But if he does, he can, he can he can follow us up and provide more clarity. I think we'll say I just looked it up. The South Polar acn basin on the Moon impact crater. Yeah, you said two and a half thousand kilometers, the biggest in the Solar system. The object they think was about two hundred kilometers in diameter. That's a bit hit on a small moon. It is type of situation. Yeah, made a bit of a mess by the sound of it. Rusty, thank you. If you want to kind of come back to us. Yeah, by all means, send us a bit more info so that we can revisit that question and don't forget. If you've got a question for us, send us in because we are a bit short, because I did a bit of a clean out when I got back and we need some fresh material. So send the questions into us via our website, Spacenuts podcast dot com or space Nuts dot io and just that little AMA link at the top is where you can send text and audio questions, which is pretty easy. If you've got a device with a. Microphone, whether that's a smartphone or a tablet or a computer, send it into us. Don't forget, forget as always to tell us who you. Are and where you're from. We're all done, Fred, Thank you so much. Oh it's been a pleasure as always and always stimulating and good to chat it is. I love it all right, We'll see you soon. Professor Fred Watson, Astronomer at large, and thanks to you in the studio who couldn't be with us today because that's his preferred state. He just doesn't want to be with us. Thanks Hugh, and from me Andrew Uncley, thanks for your company. See you on the very next episode of Space Nuts. By listen to the Space Nuts podcast. Available at Apple Podcasts, Spotify, iHeartRadio, or your favorite podcast player. You can also stream on demand at bides dot com. This has been another quality podcast production from Nights dot com.